Topic Contents

Types of Fungal Nail Infection

Topic Overview

There are four major types of
fungal nail infection. They are named for the area
where the fungal infection starts. Dermatophytes cause almost all fungal nail
infections.

Distal subungual onychomycosis (DSO) is the
most common type of fungal nail infection. It is caused by the same fungi that
cause most cases of
athlete's foot (dermatophytes). DSO infects the skin
under the end of the nail (nail bed) and in the nail. The infection starts at
the end of the nail bed, and part of the nail often turns yellow or white.
Pieces of skin and nail fragments (debris) build up under the nail. As the
condition gets worse, the nail may crumble and split, and it may separate from
the skin. A thickened nail and a large amount of debris under the nail may
cause discomfort when wearing shoes. DSO can be a lifelong infection and hard
to treat. Shoes that fit poorly may make the infection worse or, in some cases,
even cause the infection.

White superficial onychomycosis (WSO), the
second most common type of fungal nail infection. It can be easily treated. WSO
affects the top layer of the nail, first forming white spots on the nail
surface. Eventually the entire surface of the nail becomes covered with a
crumbly, chalky powder. The nail does not thicken and does not separate from
the skin.

Candida onychomycosis, or yeast infection of
the nail, is uncommon but can affect the nail and the skin bordering the nail
(nail folds). This type of fungal infection is more common in fingernails than
toenails. It may involve all of the nails at the same time and can cause the
nail to separate from the nail bed. It invades weakened areas of the nail,
which may become discolored white, green, or brownish, with an odd shape. The
nail may look thicker than normal, and there may be signs of infection
(reddened, swollen, tender, or warm) in the skin next to the nail (nail fold).
Unlike the other types of fungal nail infections, the infection may be
painful.

Proximal subungual onychomycosis (PSO) is
caused by dermatophytes. It is more common in people infected
with the
human immunodeficiency virus (HIV). PSO infects the base of the nail (skin at the nail fold),
often thickening the skin, which can separate from the nail. The base of the
nail may appear white, and the nail opaque. The skin on top of the foot may
become infected.

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